1. Field of the Invention
The present invention relates to a heat exchanger preferably used for exchanging heat between hot water to be supplied, which flows in tubes, and a combustion gas which flows in a fin region interposed between the tubes.
2. Description of the Related Art
Concerning the conventional heat exchanger, for example, JP-A-2003-106794 discloses a well known heat exchanger. This heat exchanger exchanges heat between the exhaust gas, which is discharged from an internal combustion engine, and the cooling water. In this heat exchanger, a plurality of wings (louvers, in this document) are provided in the exhaust gas flow direction on the inner wall side of the exhaust gas passage of the wave-shaped fins arranged in the exhaust gas passage.
Each wing is formed out of a face, the distance from the inner wall side of which is increased as it comes to the downstream side of the exhaust gas flow, arranged crossing the flow direction of the exhaust gas.
Due to the foregoing, vertical vortexes are formed when the exhaust gas moves over the wings. The vertical vortexes are drawn onto the inner wall side on the downstream side by a pressure difference between the side of the wing on the upstream side and the side of the wing on the downstream side. At the same time, the vertical vortexes are accelerated. Further, the exhaust gas passing in a gap, which is formed between the vertical plate section of the fins crossing the inner wall and the wings, is also accelerated by the vertical vortexes. Therefore, the heat transfer coefficient on the exhaust gas side can be enhanced and, further, an unburned substance, such as soot, attached to the fins can be blown away. Accordingly, while the fins are being prevented from clogging, the heat exchanging efficiency can be enhanced.
However, when the distribution of the flow velocity was analyzed in detail in the entire fin region in which a plurality of wings were arranged, the following results were obtained. In the heat exchanger of the present invention described later, as shown in FIG. 8, on the upstream side of the external fluid (combustion gas), it was possible to confirm the effect of the wings 123. However, as it came to the downstream side, the external fluid flowed being separated from the wing 123, and the generation of the vertical vortexes was attenuated and the flow velocity was lowered in the wing portions 123. Investigations were also made into the heat flux as follows. As shown in FIG. 9, the same result as that of the above flow velocity distribution was obtained. That is, it was found that a sufficiently high effect of the wings 123 was not obtained. In this connection, FIGS. 8A to 8D are views respectively showing the flow velocity distributions (The flow velocity on the flow-in side is 7 m/s.) in the root portion, the middle portion and the forward end portion of the wings 123 and also showing the flow velocity distribution of the middle portion of the fin 120. FIG. 9A is a view showing a heat flux distribution on the left of the vertical plate portion 122 of the fin 120 in FIG. 9B, FIG. 9B is a view showing a heat flux distribution on the flat plate portion 121 on the inner wall side of the fin 120, and FIG. 9C is a view showing a heat flux distribution on the right of the vertical plate portion 122 of the fin 120 in FIG. 9B.